1. Field of the Invention
This invention relates generally to apparatuses for spraying or coating a lubricant onto the surfaces of a cutting tool. More particularly, it relates to a device for applying electrostatically charged lubricant of a high resistivity to the active surfaces of cutting tools.
As is generally well-known in the art of machining operations such as drilling, milling, sawing and the like, when the tool is applied to the workpiece there is created large amounts of heat due to their frictional interengagement. This heat is highly undesirable since it leads to the shortening of the useful life of the cutting tool. In order to prolong the life of the tools, it has been known in industrial practice that special high lubricity cutting lubricants can be applied to the contact area between the tool and the workpiece. Further, it is generally known that only a small amount of such lubricants is required so as to achieve this result.
One of the current techniques is to apply the lubricant material by brushing or blowing single drops thereof, such as by using air nozzles, onto the cutting surfaces of the cutting tools. However, this prior art technique suffers from the disadvantage of being cumbersome since it is a very time-consuming process. Further, this technique also has the problem of requiring the use of multiple nozzles when the cutting tool has more than one dimension, thereby increasing its complexity and cost. In addition, there is still another disadvantage encountered with such air nozzles since they consume significant amounts of shop air which is relatively expensive.
2. Description of the Prior Art
The literature is replete with numerous types of electrostatic atomizing devices which are of limited relevancy to the instant application due to a number of factors such as the inability to be functionally operable with a moderately low high-voltage electric potential and the inability to atomize liquids with high resistivity.
In U.S. Pat. No. 3,556,255 to George F. Lomax, Jr. issued on Jan. 19, 1971, there is disclosed an apparatus for applying dry, solid lubricant particles onto the work surface of a forge tool which includes a source of solid lubricant particles, an electrostatic charging chamber and a nozzle. The source of solid particles is interconnected between a gas supply and one end of the charging chamber. The charging chamber is also connected to a potential supply. The nozzle is connected to the other end of the charging chamber for spraying charged particles onto the surface of the forge tool.
In U.S. Pat. No. 3,735,925 to Gyorgy Benedek et al. issued on May 29, 1973, there is disclosed an apparatus for electrostatically charging material to be sprayed onto a surface which includes a first electrode of a condenser having a high-voltage of 15-20 kV connected thereto and a second electrode being grounded. The second electrode is positioned opposite the first electrode at a spaced-apart interval therebetween and is covered with a dielectric. The material to be sprayed is passed through the two electrodes to create a uniform electrostatic charging effect prior to spraying.
In U.S. Pat. No. 4,776,515 to Michael Michalchik issued on Oct. 11, 1988, there is described an apparatus for generating a mist of negatively charged liquid particles which includes a liquid container, a capillary tube in fluid communication with the container, an electrode at least partially within a passage of the capillary tube and a DC power supply supplying a negative potential. The liquid is indicated to have a resistivity in the range of 1.6.times.10.sup.3 to 4.0.times.10.sup.5 Ohms-cm, and the negative potential is specified to have an operating range between 5 and 8 kV DC.
U.S. Pat. No. 4,004,733 to S. Edward Law issued on Jan. 25, 1977, is directed to an electrostatic spray nozzle formed of a base having a central conduit for receiving liquid under pressure and having a forwardly extending conduit to receive air under pressure, and a housing fixedly secured to the base. The housing has a forwardly extending nozzle passage and is in fluid communication with the air and liquid conduits of the base. An annular electrode is disposed within the housing and is coaxial with the nozzle passage. The electrode is operated at a relatively low voltage (i.e., 2 kV) so as to impart a high spray-cloud charge to the stream of liquid droplets formed in the nozzle passage.
U.S. Pat. No. 4,168,327 to S. Edward Law issued on Sep. 18, 1979, is directed to a space-charge controlled electrostatic spraying method which uses a low volume spray nozzle to produce finely divided, electrostatically charged particles. The charged particles are monitored to sense the value of a parameter related to their space-charge density. The particles are first deposited on a calibration target simulating the ultimate target object, and the space-charge density of the stream is varied while the degree and/or quality of the deposition on the test objects is measured. The space-charge density corresponding to the optimal deposition is thereafter maintained while the charged particles are being deposited onto the target object.
In U.S. Pat. No. 4,255,777 to Arnold J. Kelly issued on Mar. 10, 1981, there is disclosed an electrostatic charging device for electrostatically atomizing fluids into a plurality of charged droplets which includes a housing a having a chamber therein and the fluid is disposed within the chamber. First and second electrodes are disposed in a spaced-apart relationship to each other and are in liquid contact with fluid within the chamber so as to generate an electric charge. The first electrode may consist of an elongated rod with a sharp tipped end, and the second electrode may be provided with a blunt end. The first electrode is connected to a high voltage source, and the second electrode is connected via a resistor element to the opposite end of a high voltage source. The high voltage is stated to be most preferably between 100 volts to about 30 kilovolts D.C. A ground electrode is disposed externally to the housing and forms an electrostatic field so as to assist the spraying of the charged droplets. The fluid is stated to have a conductivity most preferably less than about 10.sup.-10 mho/meter.
German patent application No. P27 31 712.0 to Ronald A. Coffee filed Jul. 13, 1977, is directed to an electrostatic liquid atomizer which includes a plastic tube for housing a high voltage supply and a switch. At the front end of the tube, there is provided a bracket having a threaded hole for receiving a bottle containing the liquid to be atomized. A tubular distributor has its upper end connected to the bottom of the hole in the bracket and has its lower end connected to a plate. The plate is formed with a plurality of capillary tubes which function as a nozzle. One end of a blank wire is soldered to the capillary tube, and the other end thereof is connected to the high voltage terminal of the high voltage supply. The distributor is further inserted through the bottom of an inverted cup. A field steering electrode in the form of a metal ring is attached to the rim of the cup and is grounded by way of a grounding wire. The high voltage is in the range of 1 to 20 kV. The liquids used during the testing of the device had a resistivity between 1.times.10.sup.7 and 5.times.10.sup.8 Ohms-cm.
British patent No. 2,114,686B to Adrian G. Bailey et al. issued on Apr. 30, 1986, is directed to an apparatus for supplying of lubricant to a workpiece during a machining operation which includes a stationary electrically conductive lubricant discharge nozzle. A wire is connected to the nozzle for supplying an elevated electrical potential from a high voltage supply unit. The nozzle is enclosed by a molded insulating and protective shroud so that only the tip thereof is exposed. The tip is described to be preferably a relatively sharp edge. A high voltage supply unit is operated between 6-10 kV. The liquid is specified to have an electrical conductivity within the approximate range of 10.sup.-8 Sm.sup.-1 to 10.sup.-3 Sm.sup.-1 so as to provide satisfactory charging and atomization.
The prior art reveals that it is well known that liquids can be electrostatically atomized utilizing capillaries. The prior art patents teach that materials with low resistivity such as water and water alcohol mixtures having substantial concentrations of water or alcohol and materials with moderate resistivity such as paints and some solvent oils can be atomized and projected electrostatically. However, the prior art fails to show that materials with a very high resistivity such as kerosene and high lubricity lubricants can be electrostatically charged and atomized. This is because of the fact that there is not sufficient time for the electric charge to flow and segregate in the high resistivity liquid before drops form from the bulk liquid. Further, the high resistivity of liquid serves to retard the current flow even when very high electric potentials are applied.
As used herein, low resistivity materials refer to those with a resistivity below 10.sup.5 Ohm meters. Further, moderate resistivity materials refer to those with a resistivity in the range of 10.sup.5 to 10.sup.8 Ohm meters (sometimes defined as good "spraying liquids"), and high resistivity materials refer to those with a resistivity above 10.sup.8 Ohm meters.